Alkali-free glass

ABSTRACT

An alkali-free glass includes, in mol % in terms of oxides: SiO 2 : 63-75%; Al 2 O 3 :10-16%; B 2 O 3 : larger than 0.5% and 5% or smaller; MgO: 0.1-15%; CaO: 0.1-12%; SrO: 0-8%; and BaO: 0-6%. [MgO]/[CaO] is larger than 1.5. A value of Formula (A) is 82.5 or larger. A value of Formula (B) is 690 or larger and 800 or smaller. A value of Formula (C) is 100 or smaller. A value of Formula (D) is 20 or smaller. The alkali-free glass has a Young&#39;s modulus of 83 GPa or larger and a surface devitrification viscosity η c  of 10 4.2  dPa·s or higher.

TECHNICAL FIELD

The present invention relates to alkali-free glass that is suitable forsubstrate glass etc. for various displays, photomasks, support forelectronic devices, information recording media, planar antennas,dimming laminates, vehicular window glasses, and acoustic vibrationplates, etc.

BACKGROUND ART

Conventionally, glass that is used for glass plates (glass substrates)for various displays, photomasks, support for electronic device andinformation recording media, in particular glass used for glass plateson the surfaces of which a thin-film of a metal, an oxide, or the likeis to be formed, is required to have the following properties (1) to(4).

-   (1) The glass contains substantially no alkali metal ions. This is    because if glass contains alkali metal oxides, alkali metal ions    diffuse through the above-described thin film and degrade the film    characteristics of the thin film.-   (2) The strain point is high so that shrinkage (compaction) that    accompanies deformation of a glass plate and stabilization of the    glass structure occurring when the glass plate is exposed to a high    temperature in a thin-film forming process can be minimized.-   (3) The chemical durability against various chemicals used for    formation of a semiconductor is sufficiently high. In particular,    the glass is durable against buffered hydrofluoric acid (BHF: a    mixed liquid of hydrofluoric acid and ammonium fluoride) for etching    of SiO_(x) and SiN_(x), liquid chemicals containing hydrochloric    acid and used for ITO etching, various kinds of acids (nitric acid,    sulfuric acid, etc.) used for etching a metal electrode, alkalis of    resist peeling liquids, etc.-   (4) No defects (bubbles, striae, inclusions, pits, scratches, etc.)    exist inside or in the surface.

In addition to the above requirements, the following requirements (5) to(9) have been imposed further in recent years:

-   (5) Glass itself that is small in specific gravity is desired    because displays etc. are required to be reduced in weight.-   (6) Thickness reduction of glass plates are desired because displays    etc. are required to be reduced in weight.-   (7) High heat resistance is desired because polysilicon (p-Si; high    in heat treatment temperature) type liquid crystal displays have    come to be manufactured in addition to conventional amorphous    silicon (a-Si) type liquid crystal displays. The heat resistance of    a-Si is about 350° C. and that of p-Si is 350-550° C.-   (8) To increase the productivity by increasing the temperature    rising and dropping rates in fabrication of a display or the like or    to increase the thermal shock resistance, glass that is small in    average thermal expansion coefficient is required. On the other    hand, in the case where the average thermal expansion coefficient of    glass is too small, if the number of processes for forming various    films such as a gate metal film and a gate insulating film in    manufacturing a display or the like is large, the glass is increased    in warp, leading to problems, for example, causing troubles such as    occurrence of breaking or a scratch during transport of the display    or the like and large deviation of exposure patterns.-   (9) Furthermore, in recent years, with size increase and thinning of    glass substrates, glass having a large specific modulus ((Young's    modulus)/density) has been required.

To satisfy requirements as described above, various glass compositionshave been proposed so far for, for example, glass for a display panel(refer to Patent Literatures 1-4).

In recent years, the resolution of electronic displays is furtherincreasing. With the increase in resolution, large-size TVs have aproblem that the substrate is increased in warp by formation of variouskinds of films (e.g., due to film thickness increase of Cuinterconnections). This has increased the need for a substrate that issmall in warp and, to fulfill this need, it is necessary to increase theYoung's modulus of glass.

However, glass having a large Young's modulus as disclosed in PatentLiterature 3 or 4 is high in strain point and its devitrificationtemperature tends to be higher than a temperature T₄ at which the glassviscosity becomes 10⁴ dPa·s. This makes it difficult to form glass andit is worried that a resulting increased load on manufacturingfacilities may increase the manufacturing cost.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 5702888

Patent Literature 2: WO 2013/183626

Patent Literature 3: Japanese Patent No. 5849965

Patent Literature 4: Japanese Patent No. 5712922

SUMMARY OF INVENTION Technical Problem

The present inventors have also found the following items to worryabout.

As described above, a high strain point or devitrification temperaturemakes glass manufacture difficult, and it has been found that a highcrystal growth rate also raises a problem of difficulty in glassmanufacture. More specifically, in the case where the crystal growthrate is high, crystals that have been deposited during a long-termmanufacture are mixed into glass and become foreign matter defects.Foreign matter defects mixed into glass may become, even if they areextremely small, origins of fracture of a substrate in handling alarge-size substrate, for example. Therefore it is important to lowerthe crystal growth rate. Incidentally, the present inventors have foundthat the crystal growth rate and the devitrification temperature have nocorrelation; that is, the crystal growth rate and the devitrificationtemperature are independent characteristics. It is therefore difficultto obtain high-quality alkali-free glass at a high productivity if thecrystal growth rate is high even when glass having a low devitrificationtemperature is used.

An object of the present invention is to provide glass that is low incrystal growth rate and even higher in productivity and quality inaddition to being able to reduce deformation, such as a warp, of a glasssubstrate and being high in formability and low in the load onmanufacturing facilities.

Solution to Problem

To attain the above object, the invention provides alkali-free glass(1), containing in mol % in terms of oxides:

SiO₂: 63-75%;

Al₂O₃: 10-16%;

B₂O₃: larger than 0.5% and 5% or smaller;

MgO: 0.1-15%;

CaO: 0.1-12%;

SrO: 0-8%; and

BaO: 0-6%,

in which:

[MgO]/[CaO] is larger than 1.5;

a value of Formula (A) is 82.5 or larger, Formula (A) being1.131[SiO₂]+1.933 [Al₂O₃]+0.362[B₂O₃]+2.049[MgO]+1.751 [CaO]+1.471 [SrO]+1.039[BaO]−48.25;

a value of Formula (B) is 690 or larger and 800 or smaller, Formula (B)being35.59[SiO₂]+37.34[Al₂O₃]+24.59[B₂O₃]+31.13[MgO]+31.26[CaO]+30.78[SrO]+31.98[BaO]−2761;

a value of Formula (C) is 100 or smaller, Formula (C) being−9.01[SiO₂]+36.36[Al₂O₃]+5.7[B₂O₃]+5.13[MgO]+17.25[CaO]+7.65[SrO]+10.58[BaO];

a value of Formula (D) is 20 or smaller, Formula (D) being{−0.731[SiO₂]+1.461[Al₂O₃]−0.157[B₂O₃]+1.904[MgO]+3.36[CaO]+3.411[SrO]+1.723[BaO]+(−3.318[MgO][CaO]−1.675[MgO][SrO]+1.757[MgO][BaO]+4.72[CaO][SrO]+2.094[CaO][BaO]+1.086[SrO][BaO])}/([MgO]+[CaO]+[SrO]+[BaO]);and

the alkali-free glass has a Young's modulus of 83 GPa or larger and asurface devitrification viscosity η_(c) of 10^(4.2) dPa·s or higher.

In the alkali-free glass (1) according to the invention, a value ofFormula (E) is preferably within a range of 1.50 to 5.50, Formula (E)being4.379[SiO₂]+5.043[Al₂O₃]+4.805[B₂O₃]+4.828[MgO]+4.968[CaO]+5.051[SrO]+5.159[BaO]−453.

The alkali-free glass (1) according to the invention preferably has astrain point of 690° C. or higher.

The alkali-free glass (1) according to the invention preferably has adensity of 2.8 g/cm³ or lower and an average thermal expansioncoefficient in 50-350° C. of 30×10⁻⁷/° C. to 45×10⁻⁷/° C.

The alkali-free glass (1) according to the invention preferably has atemperature T₂ at which a glass viscosity becomes 10² dPa·s of 1800° C.or lower and a temperature T₄ at which the glass viscosity becomes 10⁴dPa·s of 1400° C. or lower.

The alkali-free glass (1) according to the invention preferably has aninternal devitrification temperature of 1320° C. or lower.

The alkali-free glass (1) according to the invention preferably has aninternal devitrification viscosity lid of 10^(4.4) dPa·s or higher.

The alkali-free glass (1) according to the invention, preferably has acrystal growth rate of 100 μm/hr or lower.

The alkali-free glass (1) according to the invention may contain atleast one selected from the group consisting of Li₂O, Na₂O, and K₂O inan amount of 0.2% or smaller in total in mol % in terms of oxides.

The invention also provides alkali-free glass (2), containing in mol %in terms of oxides:

SiO₂: 50-80%;

Al₂O₃: 8-20%;

Li₂O+Na₂O+K₂O: 0-0.2%; and

P₂O₅: 0-1%,

in which

[MgO]/[CaO] is larger than 1.5, and

the alkali-free glass has:

a Young's modulus of 83 GPa or larger;

a strain point of 690° C. or higher;

a temperature T₄ at which a glass viscosity becomes 10⁴ dPa·s of 1400°C. or lower;

a temperature T₂ at which the glass viscosity becomes 10² dPa·s of 1800°C. or lower;

an internal devitrification temperature of 1320° C. or lower;

an internal devitrification viscosity η_(d) of 10^(4.4) dPa·s or higher;

a surface devitrification viscosity of 10^(4.2) dPa·s or higher;

a crystal growth rate of 100 μm/hr or lower;

a density of 2.8 g/cm³ or lower;

a specific modulus of 31 or higher; and

an average thermal expansion coefficient in 50-350° C. of 30×10⁻⁷/° C.to 45×10⁻⁷/° C.

The alkali-free glass (2) according to the invention preferably containsB₂O₃ in an amount of 0-5% in mol % in terms of oxides.

The alkali-free glass (2) according to the invention preferablycontains, in mol % in terms of oxides, MgO: 0.1-15%, CaO: 0.1-12%, SrO:0-8%, and BaO: 0-6%.

The alkali-free glass (2) according to the invention preferablycontains, in mol % in terms of oxides, B₂O₃: 0-5%, MgO: 0.1-15%, CaO:0.1-12%, SrO: 0-8%, and BaO: 0-6%.

In the alkali-free glass (2) according to the invention, a value ofFormula (A) is preferably 82.5 or larger, Formula (A) being 1.131[SiO₂]+1.933[Al₂O₃]+0.362[B₂O₃]+2.049[MgO]+1.751[CaO]+1.471[SrO]+1.039[BaO]″48.25.

In the alkali-free glass (2) according to the invention, a value ofFormula (B) is preferably 690 or larger and 800 or smaller, Formula (B)being35.59[SiO₂]+37.34[Al₂O₃]+24.59[B₂O₃]+31.13[MgO]+31.26[CaO]+30.78[SrO]+31.98[BaO]−2761.

In the alkali-free glass (2) according to the invention, a value ofFormula (C) is preferably 100 or smaller, Formula (C) being−9.01[SiO₂]+36.36[Al₂O₃]+5.7[B₂O₃]+5.13[MgO]+17.25[CaO]+7.65[SrO]+10.58[BaO].

In the alkali-free glass (2) according to the invention, a value ofFormula (D) is preferably 20 or smaller, Formula (D) being{-0.731[SiO₂]+1.461[Al₂O₃]−0.157[B₂O₃]+1.904[MgO]+3.36[CaO]+3.411[SrO]+1.723[BaO]+(−3.318[MgO][CaO]1.675[MgO][SrO]+1.757[MgO][BaO]+4.72[CaO][SrO]+2.094[CaO][BaO]+1.086[SrO][BaO])}/([MgO]+[CaO]+[SrO]+[BaO]).

In the alkali-free glass (2) according to the invention, a value ofFormula (E) is preferably 1.50-5.50, Formula (E) being4.379[SiO₂]+5.043[Al₂O₃]+4.805[B₂O₃]+4.828[MgO]+4.968[CaO]+5.051[SrO]+5.159[BaO]−453.

The alkali-free glass (1) and the alkali-free glass (2) according to theinvention may each contain F in an amount of 1.5 mol % or smaller.

The alkali-free glass (1) and the alkali-free glass (2) according to theinvention may each contain SnO₂ in an amount of 0.5% or smaller in mol %in terms of oxides.

The alkali-free glass (1) and the alkali-free glass (2) according to theinvention may each contain ZrO₂ in an amount of 0.09% or smaller in mol% in terms of oxides.

Each of the alkali-free glass (1) and the alkali-free glass (2)according to the invention preferably has a β-OH value of the glass of0.01 mm⁻¹ or larger and 0.5 mm⁻¹ or smaller.

Each of the alkali-free glass (1) and the alkali-free glass (2)according to the invention, preferably has an annealing point of 850° C.or lower.

In each of the alkali-free glass (1) and the alkali-free glass (2)according to the invention, a compaction is preferably 150 ppm orsmaller when being held at 600° C. for 80 min. p Each of the alkali-freeglass (1) and the alkali-free glass (2) according to the inventionpreferably has an equivalent cooling rate of 5° C./min or higher and800° C./min or lower.

In each of the alkali-free glass (1) and the alkali-free glass (2)according to the invention, a sludge volume when it is subjected to anetching process is preferably 30 ml or smaller.

Each of the alkali-free glass (1) and the alkali-free glass (2)according to the invention, preferably has a photoelastic constant of 31nm/MPa/cm or smaller.

The invention provides a glass plate including the alkali-free glass (1)or the alkali-free glass (2) according to the invention, whichpreferably has a length of at least one side of 2400 mm or longer andthe thickness of 1.0 mm or smaller.

The glass plate according to the invention is preferably manufactured bya float process or a fusion process.

Furthermore, the invention provides a display panel including thealkali-free glass (1) or the alkali-free glass (2) according to theinvention.

The invention provides a semiconductor device including the alkali-freeglass (1) or the alkali-free glass (2) according to the invention.

The invention provides an information recording medium including thealkali-free glass (1) or the alkali-free glass (2) according to theinvention.

The invention provides a planar antenna including the alkali-free glass(1) or the alkali-free glass (2) according to the invention.

The invention provides a dimming laminate including the alkali-freeglass (1) or the alkali-free glass (2) according to the invention.

The invention provides a vehicular window glass including thealkali-free glass (1) or the alkali-free glass (2) according to theinvention.

The invention provides an acoustic vibration plate including thealkali-free glass (1) or the alkali-free glass (2) according to theinvention.

Advantageous Effects of Invention

The invention can provide glass that is low in crystal growth rate andeven higher in productivity and quality in addition to being able tosuppress deformation, such as a warp, of a glass substrate and beinghigh in formability and low in the load on manufacturing facilities.

DESCRIPTION OF EMBODIMENTS

Alkali-free glass according to the present invention will be hereinafterdescribed. In the following, the range of the content of each componentof glass will be expressed in mol % in terms of oxides.

However, the content of each component in Formula (A) to Formula (E) isa mole % value calculated with an assumption that the total amount ofseven components SiO₂, Al₂O₃, B₂O₃, MgO, CaO, SrO, and BaO is 100 mol %.

In the following, a numerical value range expressed in the form of “A-B”means a range including the numerical values A and B as a minimum valueand a maximum value, respectively, that is, a range that is larger thanor equal to the numerical value A and smaller than or equal to thenumerical value B.

In the case where the content of SiO₂ is smaller than 50 mol %(hereinafter written simply as “%”), there are tendencies that thestrain point is not sufficiently high and the average thermal expansioncoefficient and the specific gravity are large. Thus, the content ofSiO₂ is 50% or larger. The SiO₂ content is preferably 55% or larger,more preferably 60% or larger, more preferably 63% or larger, morepreferably 64% or larger, more preferably 65% or larger, more preferably66% or larger, particularly preferably 66.5% or larger, and mostpreferably 67% or larger.

In the case where the content of SiO₂ is larger than 80%, there aretendencies that the glass solubility is low, the Young's modulus issmall, and the devitrification temperature is high. Thus, the content ofSiO₂ is 80% or smaller. The SiO₂ content is preferably 75% or smaller,more preferably 74% or smaller, more preferably 73% or smaller, morepreferably 72% or smaller, particularly preferably 71.5% or smaller, andmost preferably 71% or smaller.

Al₂O₃ reduces a warp by increasing the Young's modulus and increases theglass strength by reducing the phase separationability so as to increasethe fracture toughness. In the case where the content of Al₂O₃ issmaller than 8%, these effects do not tend to be exhibited and thecontents of other components that increase the average thermal expansioncoefficient relatively increase, as a result of which the averagethermal expansion coefficient tends to be large. Thus, the content ofAl₂O₃ is 8% or larger. The Al₂O₃ content is preferably 8.5% or larger,more preferably 9% or larger, more preferably 9.5% or larger, morepreferably 10% or larger, more preferably 10.2% or larger, morepreferably 10.4% or larger, more preferably 10.6% or larger,particularly preferably 10.8% or larger, particularly preferably 11% orlarger, particularly preferably 11.2% or larger, and most preferably11.4% or larger.

In the case where the content of Al₂O₃ is larger than 20%, the glasssolubility may become low, the strain point may become high, and thedevitrification temperature may become high. Thus, the content of Al₂O₃is 20% or smaller. The Al₂O₃ content is preferably 18% or smaller, morepreferably 17% or smaller, more preferably 16.5% or smaller, morepreferably 16% or smaller, more preferably 15.5% or smaller, morepreferably 15% or smaller, more preferably 14.7% or smaller,particularly preferably 14.5% or smaller, and most preferably 14.3% orsmaller.

B₂O₃ can be contained in an amount of 5% or smaller because B₂O₃increases the BHF resistance, increases the glass melting reactivity,and lowers the devitrification temperature. The content of B₂O₃ ispreferably 4% or smaller, more preferably 3.5% or smaller, morepreferably 3% or smaller, more preferably 2.8% or smaller, morepreferably 2.6% or smaller, more preferably 2.5% or smaller,particularly preferably 2.4% or smaller, and most preferably 2.3% orsmaller. To exhibit the above effects, the content of B2O3 is preferablylarger than 0.5%, more preferably 0.8% or larger, more preferably 1.2%or larger, particularly preferably 1.5% or larger, and most preferably1.7% or larger.

MgO can be contained because MgO increases the Young's modulus withoutincreasing the specific gravity and hence can alleviate the warp problemby increasing the specific modulus and increases the glass strength byincreasing the fracture toughness value. MgO also increases thesolubility. In the case where the content of MgO is smaller than 0.1%,these effects do not tend to be exhibited and the thermal expansioncoefficient may become too small. Thus, the content of MgO is preferably0.1% or larger, more preferably 4% or larger, more preferably 5% orlarger, more preferably 5.5% or larger, more preferably 6% or larger,particularly preferably 6.2% or larger, and most preferably 6.5% orlarger.

However, when the MgO content is too large, the devitrificationtemperature tends to increase. Thus, the content of MgO is preferably15% or smaller, more preferably 14% or smaller, more preferably 13% orsmaller, more preferably 12% or smaller, more preferably 11.5% orsmaller, more preferably 11% or smaller, more preferably 10.5% orsmaller, particularly preferably 10% or smaller, and most preferably9.5% or smaller.

CaO has features of increasing the specific modulus to an extent next toMgO among the alkali earth metals and not lowering the strain pointexcessively, and increases the solubility like MgO. CaO can be containedsince CaO also has a feature of being less prone to increase thedevitrification temperature than MgO. These effects do not tend to beexhibited if the content of CaO is smaller than 0.1%. Thus, the CaOcontent is preferably 0.1% or larger, more preferably 3% or larger, morepreferably 3.5% or larger, more preferably 4% or larger, more preferably4.5% or larger, particularly preferably 5% or larger, particularlypreferably 5.5% or larger, particularly preferably 6% or larger, andmost preferably 7% or larger.

In the case where the content of CaO is larger than 12%, the averageexpansion coefficient becomes too large and the devitrificationtemperature becomes so high that a devitrification problem is prone toarise during glass manufacture. Thus, the CaO content is preferably 12%or smaller, more preferably 11% or smaller, more preferably 10% orsmaller, more preferably 9% or smaller, particularly preferably 8.5% orsmaller, and most preferably 8% or smaller.

SrO can be contained because SrO does not increase the glassdevitrification temperature, and increases the solubility. The contentof SrO is preferably 0.1% or larger, more preferably 0.5% or larger,more preferably 1% or larger, particularly preferably 1.2% or larger,and most preferably 1.3% or larger.

The above-described effect of SrO is lower than that of BaO, and when anSrO content is too large, the specific gravity rather increases and theaverage thermal expansion coefficient becomes too large. Thus, thecontent of SrO is preferably 8% or smaller, more preferably 6% orsmaller, more preferably 5% or smaller, particularly preferably 4% orsmaller, and most preferably 3% or smaller.

BaO can be contained because BaO does not increase the glassdevitrification temperature, and increases the solubility. The contentof BaO is preferably 0.1% or larger, more preferably 0.3% or larger,more preferably 0.5% or larger, more preferably 0.8% or larger, and morepreferably 1% or larger.

When a BaO content is too large, the specific gravity tends to increase,the Young's modulus tends to decrease, and the average thermal expansioncoefficient tends to be too large. Thus, in the alkali-free glassaccording to the invention, the content of BaO is preferably 6% orsmaller, more preferably 5.5% or smaller, more preferably 5% or smaller,particularly preferably 4.5% or smaller, and most preferably 4% orsmaller.

As [MgO]/[CaO] which is the mixing ratio of MgO to CaO increases, thespecific modulus increases. In the case where the specific modulus(Young's modulus/density) of glass is high, a large-size thin glasssubstrate can be prevented from being bent in device manufacturing lineso that a problem can be prevented. Therefore, [MgO]/[CaO] is largerthan 1.5. [MgO]/[CaO] is preferably 1.8 or larger, more preferably 2 orlarger, more preferably 2.5 or larger. [MgO]/[CaO] is preferably 20 orsmaller, more preferably 15 or smaller, particularly preferably 10 orsmaller. It is noted that the term [metal oxide] such as [MgO]represents the content in mol % of the metal oxide.

The alkali-free glass according to the invention contains substantiallyno alkali metal oxides such as Li₂O, Na₂O, and K₂O. In the invention,the expression “to contain substantially no alkali metal oxides” meansthat no alkali metal oxides are contained except unavoidable impuritiesmixed from raw materials etc., that is, no alkali metal oxides arecontained intentionally. However, alkali metal oxides may be containedat prescribed contents to obtain a particular effect (e.g., lower thestrain point, Tg, or annealing point). More specifically, at least oneselected from the group consisting of Li₂O, Na₂O, and K₂O may becontained at a total content of 0.2% or smaller in mol % in terms ofoxides. The total content is preferably 0.15% or smaller, morepreferably 0.1% or smaller, more preferably 0.08% or smaller, morepreferably 0.05% or smaller, and particularly preferably 0.03% orsmaller. At least one selected from the group consisting of Li₂O, Na₂O,and K₂O may be contained at a total content of 0.001% or larger in mol %in terms of oxides.

To prevent degradation of the characteristics of thin-film of a metal,oxide or the like formed on the surface of the glass plate when analkali-free glass plate is used in manufacture of a display, it ispreferable that the alkali-free glass according to the invention containsubstantially no P₂O₅. In the invention, the expression “to containsubstantially no P₂O₅ means that its content is, for example, 1% orsmaller, even preferably 0.5% or smaller and further preferably 0.1% orsmaller. Furthermore, to facilitate glass recycling and lower the loadon the environment, it is preferable that substantially no PbO,As₂O_(3,) or Sb₂O₃ be contained. In the invention, the expression “tocontain substantially no PbO, As₂O₃, or Sb₂O₃” means that the content ofeach of PbO, As₂O_(3,) and Sb₂O₃ is, for example, 0.01% or smaller,preferably 0.005% or smaller.

On the other hand, to increase the glass solubility, clarity,formability, etc., one or both of As₂O₃ and Sb₂O₃ may be contained at atotal content of 1% or smaller. The total content is preferably 0.5% orsmaller, more preferably 0.3% or smaller, more preferably 0.2% orsmaller, more preferably 0.15% or smaller, and more preferably 0.1% orsmaller.

To increase the glass solubility, clarity, formability, etc., thealkali-free glass according to the invention may contain one or more ofZrO₂, ZnO, Fe₂O₃, SO₃, F, Cl, and SnO₂ at a total content of 2% orsmaller, even preferably 1% or smaller and further preferably 0.5% orsmaller. Where F is contained among these substances to increase theglass solubility and clarity, the content of F is preferably 1.5% orsmaller (0.43 mass % or smaller), more preferably 1% or smaller, morepreferably 0.5% or smaller, more preferably 0.3% or smaller, morepreferably 0.1% or smaller, particularly preferably 0.05% or smaller,and most preferably 0.01% or smaller. It is noted that the F contentdoes not indicate an amount that is input to glass raw materials but anamount remaining in molted glass. This also applies to the content of Clto be described later.

In the case where SnO₂ is contained among the above substances toimprove the glass solubility and clarity, the content of SnO₂ ispreferably 0.5% or smaller (1.1 mass % or smaller).

To lower the glass melting temperature, increase the Young's modulus,and improve the resistance to chemicals, ZrO2 may be contained at 0.001%or larger (0.001 mass % or larger).

However, too large a ZrO₂ content may increase the devitrificationtemperature, increase the permittivity ε, or make glass uneven.Furthermore, in the case where glass containing ZrO₂ is applied to asemiconductor device, a failure may be caused by α rays. The content ofZrO₂ is preferably 0.09% or smaller (0.09 mass % or smaller), morepreferably 0.08% or smaller (0.08 mass % or smaller), more preferably0.07% or smaller (0.07 mass% or smaller), more preferably 0.06% orsmaller (0.06 mass % or smaller), more preferably 0.05% or smaller (0.05mass % or smaller), more preferably 0.04% or smaller (0.04 mass % orsmaller), and particularly preferably 0.03% or smaller (0.03 mass % orsmaller). It is most preferable that substantially no ZrO₂ be contained.The expression “to contain substantially no ZrO₂” means that no ZrO₂ iscontained except unavoidable impurities mixed from raw materials etc.,that is, no ZrO₂ is contained intentionally.

To increase the glass solubility, Fe₂O₃ may be contained in a range of0.001% or higher and 0.05% or smaller. In the case where the ironcontent in glass is lowered, the degree of infrared absorbance due toFe²⁺ in a melting process decreases, resulting in increase of the heatconductivity of the glass. As a result, for example when the glass ismelted by heating it by heat rays of burner flames or the like in aglass melting furnace, molten glass has a narrow temperaturedistribution and hence its convection speed becomes low, as a result ofwhich the bubble quality and the uniformity of a glass product maybecome worse. High clarity and uniformity require sufficient conventionin molten glass.

When the iron content in glass is increased, iron comes to exist in theform of Fe²⁺ or Fe³⁺ and hence the transmittance of the glass may lower.In particular, since Fe³⁺ has an absorption in a wavelength range thatis shorter than or equal to 300 nm, the ultraviolet transmittance of theglass may be lowered. To obtain glass that is 0.5 mm in plate thicknessand whose transmittance at a wavelength 300 nm is 20% or higher, the Fecontent (Fe₂O₃ conversion) is preferably 0.05% or smaller, morepreferably 0.04% or smaller, more preferably 0.03% or smaller, morepreferably 0.02% or smaller, more preferably 0.01% or smaller, morepreferably 0.008% or smaller, more preferably 0.006% or smaller, morepreferably 0.004% or smaller, and particularly preferably 0.002% orsmaller.

On the other hand, when it is desired to increase the glass solubility,the Fe content (Fe₂O₃ conversion) is preferably 0.001% or larger, morepreferably 0.002% or larger, more preferably 0.005% or larger, morepreferably 0.008% or larger, more preferably 0.01% or larger, morepreferably 0.02% or larger, more preferably 0.03% or larger, andparticularly preferably 0.04% or larger.

To increase the clarity of glass, Cl may be contained in a range of0.1-1.0%. In the case where the Cl content is smaller than 0.1%, theclarifying action during melting of glass raw materials may be lowered.The Cl content is preferably 0.15% or larger, more preferably 0.2% orlarger, more preferably 0.25% or larger, and particularly preferably0.3% or larger.

In the case where the Cl content is larger than 1.0%, the action ofpreventing size increase of a foam layer during glass manufacture may belowered. The Cl content is preferably 0.8% or smaller, more preferably0.6% or smaller.

To improve the solubility, clarity, formability, etc. of glass, obtainabsorption at a particular wavelength, or improve the density, hardness,flexural rigidity, durability, etc., the alkali-free glass according tothe invention may contain one or more of Se₂O₃, TeO₂, Ga₂O₃, In₂O₃,GeO₂, CdO, BeO, and Bi₂O₃ at a total concentration of 2% or smaller,more preferably 1% or smaller, more preferably 0.5% or smaller, morepreferably 0.3% or smaller, more preferably 0.1% or smaller,particularly preferably 0.05% or smaller, and most preferably 0.01% orsmaller. The GeO₂ content is preferably smaller than 0.1%, morepreferably 0.08% or smaller, more preferably 0.05% or smaller,particularly preferably 0.03% or smaller, and most preferably 0.01% orsmaller. It is most preferable that substantially no GeO₂ be contained.The expression “to contain substantially no GeO2” means that no GeO₂ iscontained except unavoidable impurities mixed from raw materials etc.,that is, no GeO₂ is contained intentionally.

To improve the solubility, clarity, formability, etc. of glass orimprove the glass hardness (e.g., Young's modulus), the alkali-freeglass according to the invention may contain rare earth oxides ortransition metal oxides.

The alkali-free glass according to the invention may contain, as rareearth oxides, one or more of Sc₂O₃, Y₂O₃, La₂O₃, Ce₂O₃, CeO₂, Pr₂O₃,Nd₂O₃, Pm₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃,Yb₂O₃, and Lu₂O₃ at a total content of 2% or smaller, preferably 1% orsmaller, more preferably 0.5% or smaller, more preferably 0.3% orsmaller, more preferably 0.1% or smaller, particularly preferably 0.05%or smaller, and most preferably 0.01% or smaller. The content of La₂O₃is preferably smaller than 1%, more preferably 0.5% or smaller, morepreferably 0.3% or smaller, particularly preferably 0.1% or smaller, andmost preferably 0.05% or smaller. It is most preferable thatsubstantially no La₂O₃ be contained. The expression “to containsubstantially no La₂O₃” means that no La₂O₃ is contained exceptunavoidable impurities mixed from raw materials etc., that is, no La₂O₃is contained intentionally.

The alkali-free glass according to the invention may contain, astransition metal oxides, one or more of V₂O₅, Ta₂O₃, Nb₂O₅, WO₃, MoO₃,and HfO₂ at a total content of 2% or smaller, preferably 1% or smaller,more preferably 0.5% or smaller, more preferably 0.3% or smaller, morepreferably 0.1% or smaller, particularly preferably 0.05% or smaller,and most preferably 0.01% or smaller.

To improve the glass solubility, the alkali-free glass according to theinvention may contain ThO₂ which is an actinoid oxide at a concentrationof 2% or smaller, preferably 1% or smaller, more preferably 0.5% orsmaller, more preferably 0.3% or smaller, more preferably 0.1% orsmaller, particularly preferably 0.05% or smaller, particularlypreferably 0.01% or smaller, and most preferably 0.005% or smaller.

In the alkali-free glass according to the invention, the β-OH value ispreferably 0.01 mm⁻¹ or larger and 0.5 mm⁻¹ or smaller. The β-OH value,which is an index of a water content in glass, is determined bymeasuring absorbance of a glass sample for light in a wavelength rangeof 2.75-2.95 μm and dividing a maximum absorbance value β_(max) by athickness (mm) of the sample. In the case where the β-OH value is 0.5mm⁻¹ or smaller, a compaction value (described later) that is obtainedwhen a sample is held at 600° C. for 80 min is likely to be achieved.The β-OH value is more preferably 0.45 mm⁻¹ or smaller, more preferably0.4 mm⁻¹ or smaller, more preferably 0.35 mm⁻¹ or smaller, morepreferably 0.3 mm⁻¹ or smaller, more preferably 0.28 mm⁻¹ or smaller,more preferably 0.25 mm⁻¹ or smaller, more preferably 0.23 mm⁻¹ orsmaller, more preferably 0.2 mm⁻¹ or smaller, more preferably 0.15 mm⁻¹or smaller, more preferably 0.1 mm⁻¹ or smaller, particularly preferably0.08 mm⁻¹ or smaller, and most preferably 0.06 mm⁻¹ or smaller. On theother hand, in the case where the β-OH value is 0.01 mm⁻¹ or larger, aglass strain point (described later) is likely to be achieved. In thecase, the β-OH value is more preferably 0.05 mm⁻¹ or larger, morepreferably 0.08 mm⁻¹ or larger, more preferably 0.1 mm⁻¹ or larger, morepreferably 0.13 mm⁻¹ or larger, particularly preferably 0.15 mm⁻¹ orlarger, and most preferably 0.18 mm⁻¹ or larger.

In the alkali-free glass according to the invention, the value that isrepresented by the following Formula (A) is preferably 82.5 or larger.

1.131[SiO₂]+1.933[Al₂O₃]+0.362[B₂O₃]+2.049[MgO]+1.751[CaO]+1.471[SrO]+1.039[BaO]−48.25  (A)

The value represented by Formula (A) is an index of the Young's modulusof the alkali-free glass according to the invention, and the Young'smodulus tends to be small if this value is smaller than 82.5. To obtaina large Young's modulus value in the alkali-free glass according to theinvention, the value represented by Formula (A) is preferably 83 orlarger, more preferably 83.5 or larger, more preferably 84 or larger,particularly preferably 84.5 or larger, and most preferably 85 orlarger.

In the alkali-free glass according to the invention, the value that isrepresented by the following Formula (B) is preferably 690 or larger and800 or smaller.

35.59[SiO₂]+37.34[Al₂O₃]+24.59[B₂O₃]+31.13[MgO]+31.26[CaO]+30.78[SrO]+31.98[BaO]−2761  (B)

The value represented by Formula (B) is an index of the strain point ofthe alkali-free glass according to the invention, and the strain pointtends to be high if this value is larger than 800. The load onmanufacturing facilities can be made low if the value represented byFormula (B) is 800 or smaller. For example, the surface temperature ofrollers used for glass forming can be lowered, such that the life offacilities can be elongated and the productivity can be increased. Tolower the strain point in the alkali-free glass according to theinvention, the value represented by Formula (B) is more preferably 760or smaller, more preferably 750 or smaller, particularly preferably 745or smaller, and most preferably 740 or smaller.

If this value is smaller than 690, the compaction may become too large.Thus, this value is 690 or larger. The value represented by Formula (B)is preferably 695 or larger, more preferably 700 or larger, morepreferably 710 or larger, particularly preferably 715 or larger, morepreferably 720 or larger, more preferably 725 or larger, and mostpreferably 730 or larger.

In the alkali-free glass according to the invention, the valuerepresented by the following Formula (C) is preferably 100 or smaller.

−9.01[SiO₂]+36.36[Al₂O₃]+5.7[B₂O₃]+5.13[MgO]+17.25[CaO]+7.65[SrO]+10.58[BaO]  (C)

The value represented by Formula (C) is an index of the crystal growthrate of the alkali-free glass according to the invention, and thecrystal growth rate is low if this value is 100 or smaller. To make lowthe crystal growth rate in a flow path of molten glass in thealkali-free glass according to the invention, the value represented byFormula (C) is preferably 95 or smaller, more preferably 90 or smaller,more preferably 85 or smaller, particularly preferably 80 or smaller,and most preferably 75 or smaller.

The present inventors have found that the crystal growth rate and thedevitrification temperature have no correlation; that is, the crystalgrowth rate and the devitrification temperature are independentcharacteristics. It is therefore difficult to obtain high-qualityalkali-free glass at a high productivity if the crystal growth rate ishigh even if glass having a low devitrification temperature is used.

To perform surface cleaning or decrease the plate thickness, a glassplate may be etched using an etching liquid containing hydrofluoric acid(HF), for example (hereinafter referred to as “etching treatment”).Thus, a glass plate is required to be high in workability when subjectedto etching treatment. That is, it is required that the etching treatmentspeed be in a practical range and sludge produced by the etchingtreatment be small in amount and is not prone to gel.

In the alkali-free glass according to the invention, the valuerepresented by the following Formula (D) is preferably 20 or smaller.

{−0.731[SiO₂]+1.461[Al₂O₃]−0.157[B₂O₃]+1.904[MgO]+3.36[CaO]+3.411[SrO]+1.723[BaO]+(−3.318[MgO][CaO]−1.675[MgO][SrO]+1.757[MgO][BaO]+4.72[CaO][SrO]+2.094[CaO][BaO]+1.086[SrO][BaO])}/([MgO]+[CaO]+[SrO]+[BaO])  (D)

The value represented by Formula (D) is an index of a sludge volume ofthe alkali-free glass according to the invention at the time of etchingtreatment, and the sludge volume at the time of hydrofluoric acidetching treatment, for example, is low if this value is 20 or smaller.As a result, a phenomenon that sludge produced during etching treatmentsticks to the glass surface again is prevented, such that a resultingsurface can be made uniform and a glass product that is superior insurface roughness and surface flatness can be obtained.

Furthermore, a glass product that is superior in surface cleanliness canbe provided. The value represented by Formula (D) is more preferably 18or smaller, more preferably 16 or smaller, more preferably 15 orsmaller, more preferably 14 or smaller, more preferably 13.5 or smaller,more preferably 12 or smaller, more preferably 11 or smaller,particularly preferably 10 or smaller, and most preferably 9 or smaller.

In some cases, a glass substrate is subjected to etching treatment toclean the surface of a glass plate or make a glass plate thinner. Glassis required to exhibit a proper etching rate in etching treatment.

In the alkali-free glass according to the invention, the valuerepresented by the following Formula (E) is preferably in a range of1.50-5.50.

4.379[SiO₂]+5.043[Al₂O₃]+4.805[B₂O₃]+4.828[MgO]+4.968[CaO]+5.051[SrO]+5.159[BaO]−453  (E)

The value represented by Formula (E) is an index of the etchingtreatment speed of the alkali-free glass according to the invention, andin the case where this value is 1.50 or larger, the etching treatmentspeed falls within a realistic range. However, if the etching treatmentspeed is too high, it becomes difficult to control the etchingtreatment, possibly causing a problem such as deterioration of thesurface roughness of a glass plate. In the case where this value is 5.50or smaller, such problems are not caused. The value represented byFormula (E) is more preferably 1.90 or larger, more preferably 2.00 orlarger, more preferably 2.50 or larger, more preferably 3.00 or larger,more preferably 3.20 or larger, more preferably 3.50 or larger, andparticularly preferably 4.00 or larger, most preferably 4.30 or larger.The value represented by Formula (E) is preferably 5.00 or smaller, morepreferably 4.80 or smaller and more preferably 4.60 or smaller.

The Young's modulus of the alkali-free glass according to the inventionis 83 GPa or larger. The degree of deformation of a substrate when it issubjected to external stress is reduced if the Young's modulus is inthis range. For example, a warp of a glass substrate when a film isformed on its surface can be reduced. For a specific example, inmanufacture of a TFT-side substrate of a flat panel display, a warp ofthe substrate is reduced when a gate metal film made of copper or so onor a gate insulating film made of silicon nitride or so on is formed onthe surface of the substrate. Furthermore, a warp can be reduced when,for example, the substrate size is made large. Still further, breakageof the substrate can be prevented in handling a substrate that isincreased in size. The Young's modulus is more preferably 83.5 GPa orlarger, more preferably 84 GPa or larger, more preferably 84.5 GPa orlarger, and particularly preferably 85 GPa or larger, most preferablylarger than 85 GPa. In the alkali-free glass according to the invention,a Young's modulus can be measured by an ultrasonic method. The Young'smodulus is preferably 115 GPa or smaller.

In the alkali-free glass according to the invention, the strain point ispreferably 690° C. or higher. In the case where the strain point islower than 690° C., shrinkage (compaction) that accompanies deformationof a glass plate and stabilization of the glass structure tends to occurwhen the glass plate is exposed to a high temperature in a displaythin-film forming process. The strain point is preferably 700° C. orhigher, more preferably 710° C. or higher, more preferably 720° C. orhigher, particularly preferably 725° C. or higher, and most preferably730° C. or higher. On the other hand, if the strain point is too high,it is necessary to increase the temperature of an annealing machineaccordingly, which tends to shorten the life of the annealing machine.Therefore, the strain point is preferably 800° C. or lower. Furthermore,the glass formability becomes high as the strain point lowers. Thestrain point is preferably 780° C. or lower, more preferably 760° C. orlower, more preferably 750° C. or lower, particularly preferably 745° C.or lower, and most preferably 740° C. or lower.

In the alkali-free glass according to the invention, a temperature T₄ atwhich the glass viscosity becomes 10⁴ dPa·s is preferably 1400° C. orlower. The glass formability is superior if this condition is satisfied.Furthermore, for example, the amount of vaporized substances in anatmosphere around glass can be reduced and defects in the glass can bedecreased by lowering the temperature during glass forming. Since glasscan be formed at a low temperature, the load on manufacturing facilitiescan be lowered. For example, the facility life of a float bath etc. thatare used in forming glass can be elongated and the productivity can beincreased. T₄ is preferably 1350° C. or lower, more preferably 1340° C.or lower, more preferably 1330° C. or lower, more preferably 1320° C. orlower, more preferably 1310° C. or lower, more preferably 1300° C. orlower, more preferably 1295° C. or lower, particularly preferably 1290°C. or lower, and most preferably 1285° C. or lower.

T₄ can be determined by measuring viscosity using a rotary viscometerand determining a temperature at which the viscosity becomes 10⁴ dPa·saccording to a method that is prescribed in ASTM C 965-96 (year 2017).In Examples described later, NBS710 and NIST717a were used as referencesamples for instrument calibration.

In the alkali-free glass according to the invention, a temperature T₂ atwhich the glass viscosity becomes 10² dPa·s is preferably 1800° C. orlower. In the case where T₂ is 1800° C. or lower, the glass solubilitybecomes high and the load on manufacturing facilities can be lowered.For example, the facility life of a furnace for solving glass and so oncan be elongated and the productivity can be increased. Furthermore,furnace-origin defects (e.g., spot defects and ZrO₂ defects) can bereduced. T₂ is more preferably 1770° C. or lower, more preferably 1750°C. or lower, more preferably 1740° C. or lower, more preferably 1730° C.or lower, more preferably 1720° C. or lower, more preferably 1710° C. orlower, more preferably 1700° C. or lower, particularly preferably 1690°C. or lower, and most preferably 1680° C. or lower.

In the alkali-free glass according to the invention, the internaldevitrification temperature is preferably 1320° C. or lower. The glassformability is high if this condition is satisfied. A phenomenon can beprevented that crystals are formed inside the glass during forming andthe transmittance is lowered. Furthermore, the load on manufacturingfacilities can be lowered. For example, the life of such facilities as afloat bath and a fusion to be used for forming glass can be elongatedand the productivity can be increased.

The internal devitrification temperature is more preferably 1310° C. orlower, more preferably 1300° C. or lower, more preferably 1280° C. orlower, particularly preferably 1260° C. or lower, and most preferablylower than 1240° C.

In the invention, an internal devitrification temperature can bedetermined in the following manner. That is, pulverized glass particlesare put into a platinum dish and then subjected to heat treatment for 17hours in an electric furnace that is controlled at a constanttemperature. After the heat treatment, a maximum temperature at whichcrystals are deposited inside glass and a minimum temperature at whichno crystals are deposited are determined through observation using anoptical microscope and an average value of them is employed as aninternal devitrification temperature.

In the alkali-free glass according to the invention, the glass internaldevitrification viscosity η_(d) is preferably 10^(4.4) dPa·s or higher.In this case, foreign matter defects due to devitrification are notprone to occur during forming by a fusion process or a float process.The glass internal devitrification viscosity η_(d) is more preferably10^(4.5) dPa·s or higher, more preferably 10^(4.6) dPa·s or higher,particularly preferably 10^(4.7) dPa·s or higher, and most preferably10^(4.8) dPa·s or higher.

In the invention, internal devitrification viscosity 72 _(d) can bedetermined in the following manner. That is, a glass internaldevitrification temperature is determined by the above-described methodand glass internal devitrification viscosity η_(d) is determined bymeasuring glass viscosity η at the glass internal devitrificationtemperature.

In the alkali-free glass according to the invention, the surfacedevitrification temperature is preferably 1370° C. or lower. In thiscase, superior glass formability is obtained. A phenomenon can beprevented that the transmittance lowers due to formation of crystalsinside the glass during forming. Furthermore, the load on manufacturingfacilities can be lowered. For example, the life of such facilities as afloat bath and a fusion to be used for forming glass can be elongatedand the productivity can be increased.

The surface devitrification temperature is more preferably 1360° C. orlower, more preferably 1350° C. or lower, more preferably 1340° C. orlower, more preferably 1330° C. or lower, more preferably 1320° C. orlower, more preferably 1310° C. or lower, more preferably 1300° C. orlower, more preferably 1290° C. or lower, particularly preferably 1280°C. or lower, and most preferably 1270° C. or lower.

In the invention, a surface devitrification temperature can bedetermined in the following manner. That is, pulverized glass particlesare put into a platinum dish and then subjected to heat treatment for 17hours in an electric furnace that is controlled at a constanttemperature. After the heat treatment, a maximum temperature at whichcrystals are deposited in the glass surface and a minimum temperature atwhich no crystals are deposited are determined through observation usingan optical microscope and an average value of them is employed as asurface devitrification temperature.

In the alkali-free glass according to the invention, the glass surfacedevitrification viscosity η_(c) is 10^(4.2) dPa·s or higher. In thiscase, foreign matter defects due to devitrification are not prone tooccur during forming by a fusion process or a float process. The glasssurface devitrification viscosity η_(c) is preferably 10^(4.3) dPa·s orhigher, more preferably 10^(4.4) dPa·s or higher, more preferably10^(4.5) dPa·s or higher, and particularly preferably 10^(4.6) dPa·s orhigher.

In the invention, glass surface devitrification viscosity η_(c) can bedetermined in the following manner. That is, a glass surfacedevitrification temperature is determined by the above-described methodand glass surface devitrification viscosity η_(c) is determined bymeasuring glass viscosity at the glass surface devitrificationtemperature.

In the alkali-free glass according to the invention, the crystal growthrate is preferably 100 μm/hr or lower. In this case, a phenomenon can beprevented that the life of manufacturing facilities is shortened due todeposition of crystals in a flow passage of molten glass. Furthermore,the risk that deposited crystals are mixed into glass manufactured andbecome foreign matter defects becomes lower. Incidentally, even if theyare extremely small, foreign matter defects mixed into glass possiblybecome an origin of fracture of the substrate in handling a large-sizesubstrate such as a substrate one side of which measures 2400 mm orlarger; lowering the crystal growth rate is therefore important.

In the invention, a crystal growth rate can be determined in thefollowing manner. That is, pulverized glass particles are put into aplatinum dish and then subjected to heat treatment for 17 hours in anelectric furnace that is controlled around a surface devitrificationtemperature, thereby preparing plural primary crystal samples in whichminute primary crystals are deposited in the glass surface. The producedprimary crystal samples are held for 1-4 hours at temperatures havingintervals 20° C. in such a temperature range that the glass viscositybecomes 10⁴-10⁶ dPa·s, so that crystals are grown at each of the holdingtemperatures. Lengths of longest portions of crystal grains obtainedbefore and after the holding at each holding temperature are measured, adifference between the crystal sizes obtained before and after theholding at each holding temperature is determined, and a crystal growthrate at each holding temperature is determined by dividing the crystalsize difference by the holding time. In the invention, a maximum valueof the growth rates in such a temperature range that the glass viscositybecomes 10⁴-10⁶ dPa·s is employed as a crystal growth rate.

The crystal growth rate is more preferably 80 μm/hr or lower, morepreferably 65 μm/hr or lower, particularly preferably 50 μm/hr or lower,and most preferably 40 μm/hr or lower.

In the alkali-free glass according to the invention, the density ispreferably 2.8 g/cm³ or lower. In this case, self-weight gravitydeflection becomes small and handling of a large-size substrate is madeeasier. Furthermore, the weight of a device using glass can be reduced.The density is more preferably 2.7 g/cm³ or lower, more preferably 2.68g/cm³ or lower, more preferably 2.65 g/cm³ or lower, more preferably2.63 g/cm³ or lower, and particularly preferably lower than 2.6 g/cm³.The term “large-size substrate” means, for example, a substrate at leastone side of which is 2400 mm or longer.

In the alkali-free glass according to the invention, the specificmodulus ((Young's modulus)/density) of glass is preferably 31 or larger.Increasing the specific modulus ((Young's modulus)/density) of glassmakes it possible to prevent occurrence of trouble due to a warp of alarge and thin glass substrate in a device manufacturing line. Thespecific modulus ((Young's modulus)/density)) of glass is preferably31.5 or larger, more preferably 32 or larger, more preferably 32.2 orlarger, more preferably 32.4 or larger, more preferably 32.6 or larger,particularly preferably 32.8 or larger, and most preferably 33 orlarger.

In the alkali-free glass according to the invention, the average thermalexpansion coefficient in a temperature range of 50-350° C. is preferably30×10⁻⁷/° C. or larger. For example, in manufacture of a TFT-sidesubstrate of a flat panel display, there is a case where a gate metalfilm made of copper or so on, and a gate insulating film made of siliconnitride or so on are laid in order on alkali-free glass. In the casewhere the average thermal expansion coefficient in the temperature rangeof 50-350° C. is smaller than 30×10⁻⁷/° C., thermal expansioncoefficient differences from a gate metal film made of copper or so onthat is formed on the substrate surface becomes so large as to causetrouble such as a warp of the substrate or film peeling.

The average thermal expansion coefficient in the temperature range of50-350° C. is preferably 33×10⁻⁷/° C. or larger, more preferably35×10⁻⁷/° C. or larger, more preferably 36×10⁻⁷/° C. or larger,particularly preferably 37×10⁻⁷/° C. or larger, and most preferably38×10⁻⁷/° C. or larger.

On the other hand, in the case where the average thermal expansioncoefficient in the temperature range of 50-350° C. is larger than45×10⁻⁷/° C., breakage of glass may occur in a manufacturing process ofa product such as a display. Thus, it is preferably 45×10⁻⁷/° C. orsmaller.

The average thermal expansion coefficient in the temperature range of50-350° C. is preferably 43×10⁻⁷/° C. or smaller, more preferably42×10⁻⁷/° C. or smaller, more preferably 41.5×10⁻⁷/° C. or smaller, morepreferably 41×10⁻⁷/° C. or smaller, particularly preferably 40.5×10⁻⁷/°C. or smaller, and most preferably 40.3×10⁻⁷/° C. or smaller.

In the alkali-free glass according to the invention, the compaction thatoccurs when glass is held at 600° C. for 80 min is preferably 150 ppm orsmaller. The term “compaction” means a ratio of glass thermal shrinkagethat is caused by glass structure relaxation during heating treatment.In the case where the compaction is in the above range, dimensionalvariations that are caused by deformation and structure stabilization ofglass when the glass is exposed to a high temperature in a thin-filmforming process that is executed in manufacturing any of variousdisplays can be minimized.

Compaction can be measured according to the following procedure. A glassplate sample (a sample of 100 mm (length)×10 mm (width)×1 mm (thickness)which is mirror-polished using cerium oxide) is held at a temperaturethat is a glass transition point +120° C. for 5 min and then cooled toroom temperature at a rate of 40° C./min. A whole length L1 (in thelength direction) of the sample is measured in this state. Subsequently,the sample is heated to 600° C. at a rate of 100° C./hr, held at 600° C.for 80 min, cooled to room temperature at a rate of 100° C./hr, a wholelength L2 of the sample is measured again. A ratio (L1−L2)/L1, that is,a ratio of the difference (L1−L2) between the whole lengths before andafter the heat treatment at 600° C. to the whole length L1 of the samplebefore the heat treatment at 600° C., is employed as a compaction value.The compaction value measured by the above evaluation method is morepreferably 100 ppm or smaller, more preferably 90 ppm or smaller, morepreferably 80 ppm or smaller, more preferably 75 ppm or smaller,particularly preferably 70 ppm or smaller, and most preferably 65 ppm orsmaller. The absolute value of compaction is preferably close to 0 ppm.The smaller the absolute value of compaction is, the more preferablebecause thermal shrinkage of glass is less likely to occur.

In the alkali-free glass according to the invention, to decrease thecompaction, the equivalent cooling rate is preferable set at 800° C./minor lower, for example. The definition and an evaluation method of theequivalent cooling rate are as follows. Glass that has been processedinto a cuboid measuring 10 mm×10 mm×1 mm is held at a temperature thatis a glass transition point +120° C. for 5 min using an infrared heatingtype electric furnace and then cooled to room temperature (25° C.). Whenthe glass is cooled, plural glass samples are produced for which thecooling rate is varied in a range of 1° C./min to 1000° C./min. Arefractive index n_(d) of d line (wavelength: 587.6 nm) of each of thesesamples is measured by a V block method using a precision refractometerKPR-2000 produced by Shimadzu Device Corporation. Thus-obtained n_(d)values are plotted with respect to the above-mentioned cooling rate(logarithmic scale), whereby an n_(d) calibration curve with respect tothe cooling rate is obtained. Subsequently, an n_(d) value of glass thathas been melted in an electric furnace, formed, and cooled actually ismeasured by the above method. A cooling rate corresponding to the n_(d)value thus obtained (in the invention, called an “equivalent coolingrate”) can be obtained from the above calibration curve.

The equivalent cooling rate is preferably 5° C./min or higher and 800°C./min or lower from the viewpoint of a balance between compaction andproductivity. From the viewpoint of productivity, the equivalent coolingrate is more preferably 10° C./min or higher, more preferably 15° C./minor higher, particularly preferably 20° C./min or higher, and mostpreferably 25° C./min or higher. From the viewpoint of compaction, theequivalent cooling rate is more preferably 500° C./min or lower, morepreferably 300° C./min or lower, more preferably 200° C./min or lower,particularly preferably 150° C./min or lower, and most preferably 100°C./min or lower.

In the alkali-free glass according to the invention, the sludge volumeat the time of etching treatment is preferably 30 ml or smaller. In thecase where the sludge volume at the time of etching treatment is in theabove range, a phenomenon that sludge produced during etching treatmentsticks to the glass surface again is prevented, and the surface can betreated uniformly. As a result, a glass product that is superior insurface roughness and surface flatness can be obtained. Furthermore, aglass product that is superior in surface cleanliness can be obtained.The sludge volume is more preferably 20 ml or smaller, more preferably15 ml or smaller, more preferably 12 ml or smaller, particularlypreferably 10 ml or smaller, and most preferably 8 ml or smaller.

In the invention, a sludge volume at the time of etching treatment canbe determined in the following manner.

A mass of an alkali-free glass substrate 1 which has a thickness of 0.5mm and has been cut into 20 mm×30 mm is measured after being cleaned anddried. An aqueous solution (liquid chemical) adjusted so as to contain 5mass % hydrofluoric acid and 2 mass % hydrochloric acid is put into acontainer made of Teflon (registered trademark) and held at 40° C. usinga constant temperature bath. The entire alkali-free glass substrate 1 isimmersed in the liquid chemical and melted completely. To compensate forhydrofluoric acid consumed by the etching, 1.8 ml of 50 mass %hydrofluoric acid is added to the above liquid chemical. Then, a newalkali-free glass substrate 2 of 20 mm×30 mm×0.5 mm (thickness) isimmersed in the liquid chemical and also melted completely. Furthermore,1.8 ml of 50 mass % hydrofluoric acid is added to the liquid chemical, anew alkali-free glass substrate 3 of 20 mm×30 mm×0.5 mm (thickness) isimmersed in the liquid chemical and melted completely according to thesame procedure. The liquid chemical in which the alkali-free glasssubstrates have been melted is held for one day and night (24 hours)while being stirred by a magnetic stirrer, thereby producing sludge(insoluble matter) in the liquid chemical. To prevent evaporation of theliquid chemical, a lid made of Teflon (registered trademark) is put onthe container during the test. Subsequently, the liquid chemical andsludge contained in the container made of Teflon (registered trademark)are transferred to a graduated cylinder and held for 24 hours toprecipitate sludge. A volume of the sludge is measured using the scaleof the graduated cylinder and employed as a sludge volume.

In the alkali-free glass according to the invention, the etching rate ofetching treatment is preferably 5.5 μm/min or lower. If the etchingtreatment speed is too high, it may become difficult to control theetching treatment, which may cause a problem such as worsening of thesurface roughness of a glass plate. The etching rate is more preferably5.0 μm/min or lower, more preferably 4.5 μm/min or lower, particularlypreferably 4.2 μm/min or lower, most preferably 4.0 μm/min or lower. Theetching rate of etching treatment is preferably 2.40 μm/min or higher.In the case where the etching rate of etching treatment is in the aboverange, the etching treatment speed falls within a realistic range. Theetching rate of etching treatment is more preferably 2.50 μm/min orhigher, more preferably 2.70 μm/min or higher, particularly preferably2.90 μm/min or higher, and most preferably 3.00 μm/min or higher.

In the invention, an etching rate of etching treatment can be determinedin the following manner.

A mass of an alkali-free glass substrate which has a thickness of 0.5 mmand has been cut into 20 mm×30 mm is measured after being cleaned anddried. An aqueous solution (liquid chemical) adjusted so as to contain 5mass % hydrofluoric acid and 2 mass % hydrochloric acid is put into acontainer made of Teflon (registered trademark) and held at 40° C. usinga constant temperature bath. The entire alkali-free glass substrate isimmersed in the liquid chemical for 20 minutes. After the immersedalkali-free glass substrate is cleaned by pure water and dried, a massof the glass substrate is measured. An etching rate per unit time iscalculated by calculating a surface area using the dimensions of thesample, dividing a mass reduction by a density, dividing a resultingquotient by the surface area, and then dividing a resulting quotient bythe immersion time.

In the alkali-free glass according to the invention, the annealing pointis preferably 850° C. or lower. In the case where the annealing point is850° C. or lower, the load on manufacturing facilities can be lowered.For example, the surface temperature of rollers used for glass formingcan be lowered, so that the life of facilities can be elongated and theproductivity can be increased. The annealing point is more preferably820° C. or lower, more preferably 810° C. or lower, more preferably 800°C. or lower, particularly preferably 790° C. or lower, and mostpreferably 780° C. or lower. The annealing point is preferably 700° C.or higher.

In the alkali-free glass according to the invention, the glasstransition point is preferably 850° C. or lower. In the case where theglass transition point is 850° C. or lower, the load on manufacturingfacilities can be lowered. For example, the surface temperature ofrollers used for glass forming can be lowered, so that the life offacilities can be elongated and the productivity can be increased. Theglass transition point is more preferably 820° C. or lower, morepreferably 810° C. or lower, more preferably 800° C. or lower,particularly preferably 790° C. or lower, most preferably 780° C. orlower. The glass transition point is preferably 690° C. or higher.

In the alkali-free glass according to the invention, the photoelasticconstant is preferably 31 nm/MPa/cm or smaller.

In some cases, stress that occurs in a liquid crystal displaymanufacturing process and during use of a liquid crystal display devicecauses a glass substrate to exhibit birefringence, as a result of whicha display in black turns gray, and thus the contrast of the liquidcrystal display is lowered. This phenomenon can be prevented if thephotoelastic constant is 31 nm/MPa/cm or smaller. The photoelasticconstant is more preferably 30 nm/MPa/cm or smaller, more preferably 29nm/MPa/cm or smaller, more preferably 28.5 nm/MPa/cm or smaller, andparticularly preferably 28 nm/MPa/cm or smaller.

Taking into consideration the ease of ensuring other physicalproperties, the photoelastic constant is preferably 23 nm/MPa/cm orlarger, more preferably 25 nm/MPa/cm or larger. A photoelastic constantcan be measured at a measurement wavelength 546 nm by a disc compressionmethod.

The alkali-free glass according to the invention is suitable for use asa glass plate that is used as a large-size substrate because its Young'smodulus is preferably so large as 82.5 GPa or larger that the degree ofdeformation of a substrate with respect to external stress is reducedand the crystal growth rate is so low that mixing of foreign matter topossibly become an origin of breakage of a substrate is prevented. Theterm “large-size substrate” means, for example, a substrate at least oneside of which is 2400 mm or longer. A specific example is a glass platewhose longer side is 2400 mm or longer and shorter side is 2000 mm orlonger.

The alkali-free glass according to the invention is more suitable for aglass plate at least one side of which is 2400 mm or longer, forexample, a glass plate whose longer side is 2400 mm or longer andshorter side is 2100 mm or longer, even more suitable for a glass plateat least one side of which is 3000 mm or longer, for example, a glassplate whose longer side is 3000 mm or longer and shorter side is 2800 mmor longer, particularly suitable for a glass plate at least one side ofwhich is 3200 mm or longer, for example, a glass plate whose longer sideis 3200 mm or longer and shorter side is 2900 mm or longer, and mostsuitable for a glass plate at least one side of which is 3300 mm orlonger, for example, a glass plate whose longer side is 3300 mm orlonger and shorter side is 2950 mm or longer.

A glass plate according to the invention the thickness of which is 1.0mm or smaller is preferable because it enables weight reduction. In thealkali-free glass according to the invention, the thickness is morepreferably 0.7 mm or smaller, more preferably 0.65 mm or smaller, morepreferably 0.55 mm or smaller, more preferably 0.45 mm or smaller, andmost preferably 0.4 mm or smaller. The thickness can be 0.1 mm orsmaller or 0.05 mm or smaller. However, from the viewpoint of preventingself-weight gravity deflection, the thickness is preferably 0.1 mm orlarger, more preferably 0.2 mm or larger.

A glass plate including alkali-free glass according to the invention canbe manufactured according to the following procedure, for example.

Raw materials of above-described components are mixed so as to havetarget contents in a glass composition, respectively, and put into amelting furnace, where they are melted by being heated to 1500-1800° C.,thereby obtaining molten glass. The molten glass thus obtained is formedinto a glass ribbon having a predetermined thickness, which is annealedand cut into glass plates.

In the alkali-free glass according to the invention, a manufacturingmethod for decreasing the compaction can be employed. More specifically,the equivalent cooling rate is preferably 500° C./min or lower, forexample. In this connection, the definition and an evaluation method ofan equivalent cooling rate are as follows. Glass that has been processedinto a cuboid of 10 mm×10 mm×1 mm is held at a temperature that is aglass transition point +120° C. for 5 minutes using an infrared heatingtype electric furnace and then cooled to room temperature (25° C.). Whenthe glass is cooled, plural glass samples are produced for which thecooling rate is varied in a range of 1° C./min to 1000° C./min. Arefractive index n_(d) of d line (wavelength: 587.6 nm) of each of thesesamples is measured by a V block method using a precision refractometerKPR-2000 produced by Shimadzu Device Corporation. Thus-obtained n_(d)values are plotted with respect to the above-mentioned cooling rate(logarithmic scale), thereby obtaining an n_(d) calibration curve withrespect to the cooling rate. Subsequently, an n_(d) value of glass thathas been subjected to such processes as melting, forming, and cooling inan actual manufacturing line is measured by the above method. A coolingrate corresponding to the n_(d) value thus obtained (in the invention,called an “equivalent cooling rate”) can be obtained from the abovecalibration curve.

The equivalent cooling rate during annealing of a glass ribbon ispreferably 5° C./min or higher and 500° C./min or lower from theviewpoint of a balance between compaction and productivity, morepreferably 10° C./min or higher and 300° C./min or lower, morepreferably 15° C./min or higher and 100° C./min or lower.

In the invention, it is preferable that molten glass be formed into aglass plate by a float process, a fusion process, or the like.

Next, a display panel according to the invention will be described.

The display panel according to the invention includes theabove-described alkali-free glass as a glass substrate. There are noparticular limitations on the display panel except that it includes thealkali-free glass according to the invention; the display panel may beany of various display panels such as a liquid crystal display panel, anorganic EL display panel, an LED (light-emitting diode) display panel.In each kind of display panel, the glass substrate of the alkali-freeglass according to the invention may be provided with a drive circuit, ascanning circuit, or the like using thin-film transistors (TFTs).

Take a thin-film transistor liquid crystal display (TFT-LCD) as anexample. It is equipped with a display surface electrode substrate(array substrate) in which gate electrode lines and a gate insulatingoxide layer are formed on its surface and pixel electrodes are formed onthe surface of the oxide layer and a color filter substrate in which RGBcolor filters and counter electrodes are formed on its surface. Cellsare formed in such a manner that a liquid crystal material is sandwichedbetween the array substrate and the color filter substrate that arepaired with each other. The liquid crystal display panel includes otherelements such as peripheral circuits in addition to those cells. Theliquid crystal display panel according to the invention employs thealkali-free glass according to the invention in at least one of the pairof substrates that constitute the cells.

Next, a semiconductor device according to the invention includes theabove-described alkali-free glass according to the invention as a glasssubstrate, more specifically, as a glass substrate for a MEMS, CMOS,CTS, or like image sensor. For another example, a semiconductor deviceaccording to the invention includes the alkali-free glass according tothe invention as a cover glass for a projection-use display device suchas a cover glass of a LCOS (liquid crystal on silicon) device.

An information recording device according to the invention includes theabove-described alkali-free glass according to the invention as a glasssubstrate, more specifically, as a glass substrate for a magneticrecording medium, an optical disc, or the like. Examples of magneticrecording media include an energy assisted magnetic recording medium anda vertical magnetic recording medium.

A planar antenna according to the invention includes the above-describedalkali-free glass according to the invention as a glass substrate, morespecifically, as a glass substrate for an antenna that is high indirectivity and reception sensitivity such as a planar liquid crystalantenna having a planar shape examples of which include a liquid crystalantenna and a microstrip antenna (patch antenna). For example, WO2018/016398 discloses a liquid crystal antenna. For example, patentapplication publications JP 2017-509266 A and JP 2017-063255 A disclosea patch antenna.

In a planar antenna, the alkali-free glass according to the inventionconstitutes an antenna installation substrate or a protection material,for example. The protection material can prevent deterioration of anantenna function due to exposure to ultraviolet light, moisture (watervapor), or water and damaging or destruction of the antenna function dueto mechanical contact.

A planar antenna having the alkali-free glass according to the inventionis more suitable for antennas for transmitting and receiving radio wavesin a radio wave band because the planar antenna can prevent radiationefficiency reduction due to alkali components and can also preventdamaging and braking because of a large Young's modulus.

“Radio waves in a radio frequency band” means radio waves in a radiowave band (e.g., 0.3-300 GHz) of microwaves, millimeter waves, etc. thatincludes radio waves in a frequency band of 3.6-29.5 GHz including radiofrequency bands for fifth generation mobile communication systems (5G)(e.g., 3.7 GHz band (3.6-4.2 GHz)), a 4.5 GHz band (4.4-4.9 GHz), and a28GHz band (27.5-29.5 GHz).

For example, WO 2019/026963 and WO 2019/107514 disclose antennas capableof receiving radio waves in a radio frequency band.

A dimming laminate according to the invention includes theabove-described alkali-free glass according to the invention as a glasssubstrate. For example, the “dimming laminate” is a dimming laminate(also called a dimming device or a dimming glass) that is equipped witha dimming function material for controlling the light transmission stateby an electrical control. Capable of shielding or freeing the field ofview of a user or controlling the inflow of infrared light, the dimminglaminate can be used as a room partitioning material, a constructionmaterial of, for example, an outside window, a video display screen,etc. For example, WO 2017/213191 and JP 2017-90617 A disclose dimminglaminates.

A vehicular window glass according to the invention includes theabove-described alkali-free glass according to the invention as a glassplate. Enabling stable transmission and reception of radio waves stablyin a radio frequency band and not being prone to be damaged or broken asdescribed above, the vehicular window glass having the alkali-free glassaccording to the invention is suitable for a window glass of anautonomous driving vehicle.

An acoustic vibration plate according to the invention includes theabove-described alkali-free glass according to the invention as a glasssubstrate. Having a large Young's modulus, the alkali-free glassaccording to the invention is suitable for acoustic uses. For example,WO 2019/070007, WO 2018/181626, and JP 2019-68368 A disclose acousticvibration plates.

EXAMPLES

Although Examples will be described below, the invention is not limitedto those Examples. In the following, Examples 1-5 and Examples 9-13 areInventive Examples and Examples 6-8 and Examples 14-16 are ComparativeExamples.

Raw materials of respective components were mixed so as to obtain atarget glass composition (unit: mol %) of each of Examples 1-16 andmelted at 1600° C. for one hour using a platinum crucible. After themelting, a molten liquid was caused to flow out onto a carbon plate,held at a temperature that is a glass transition point +30° C. for 60minutes, and cooled to room temperature (25° C.) at a rate of 1° C. perminute thereby obtaining plate-like glass. A glass plate was obtained bymirror-polishing the plate-like glass and subjected to variousevaluations. Results are shown in Tables 1 and 2. In Tables 1 and 2,each value shown in parentheses is a calculated value or an estimatedvalue. In Tables 1 and 2, “RO” means a total content of alkali earthmetal oxides.

Measurement methods of respective physical properties will be describedbelow.

(Average Thermal Expansion Coefficient)

A measurement was carried out using a differential thermal dilatometer(TMA) according to a method that is prescribed in JIS R3102 (year 1995).The measurement temperature range was room temperature to 400° C. orhigher and an average thermal expansion coefficient in a temperaturerange 50-350° C. is shown in the unit (×10⁻⁷)/° C.

(Density)

A measurement was performed on a lump of glass in an amount of about 20g not containing bubbles by a liquid weighing method according to amethod that is prescribed in JIS Z 8807 (year 2012).

(Strain Point)

A measurement was carried out by a fiber elongation method according toa method that is prescribed in JIS R3103-2 (year 2001).

(Annealing Point)

A measurement was carried out by a fiber elongation method according toa method that is prescribed in JIS R3103-2 (year 2001).

(Glass Transition Point)

A measurement was carried out by a thermal expansion method according toa method that is prescribed in JIS R3103-3 (year 2001).

(Young's Modulus)

A measurement was performed on glass that was 1.0-10 mm in thickness byan ultrasonic pulse method according to a method that is prescribed inJIS R 1602 (year 1995).

(T₂)

Viscosity was measured using a rotary viscometer and a temperature atwhich the viscosity becomes 10² dPa·was measured according to a methodthat is prescribed in ASTM C 965-96 (year 2017).

(T₄) Viscosity was measured using a rotary viscometer and a temperatureat which the viscosity becomes 10⁴ dPa·s was measured according to amethod that is prescribed in ASTM C 965-96 (year 2017).

(Surface Devitrification Temperature T_(c))

Glass was pulverized and classification was performed using a test sieveso as to obtain particles in a diameter range of 2-4 mm. The glasscullet thus obtained was subjected to ultrasonic cleaning in isopropylalcohol for five minutes, cleaned using ion exchanged water, dried, putinto a platinum dish, and then subjected to heat treatment for 17 hoursin an electric furnace that was controlled at a constant temperature.Heat treatment temperatures were set at intervals of 10° C.

After the heat treatment, the glass was removed from the platinum dishand a maximum temperature at which crystals were deposited in the glasssurface and a minimum temperature at which no crystals were depositedwere determined through observation using an optical microscope.

Each of a maximum temperature at which crystals were deposited in theglass surface and a minimum temperature at which no crystals weredeposited was measured once. In the case where it was difficult to judgewhether crystals were deposited, measurement was possibly done twotimes.

An average value of the measured maximum temperature at which crystalswere deposited in the glass surface and the measured minimum temperatureat which no crystals were deposited was determined as a glass surfacedevitrification temperature T_(c).

(Surface Devitrification Viscosity η_(c)) A glass surfacedevitrification temperature T_(c) was determined by the above method andglass surface devitrification viscosity η_(c) was determined bymeasuring glass viscosity at the glass surface devitrificationtemperature T_(c).

(Internal Devitrification Temperature T_(d))

Glass was pulverized and classification was performed using a test sieveso as to obtain particles in a diameter range of 2-4 mm. The glasscullet thus obtained was subjected to ultrasonic cleaning in isopropylalcohol for five minutes, cleaned using ion exchanged water, dried, putinto a platinum dish, and then subjected to heat treatment for 17 hoursin an electric furnace that was controlled at a constant temperature.Heat treatment temperatures were set at intervals of 10° C.

After the heat treatment, the glass was removed from the platinum dishand a maximum temperature at which crystals were deposited in the glasssurface and a minimum temperature at which no crystals were depositedwere determined through observation using an optical microscope.

Each of a maximum temperature at which crystals were deposited insidethe glass and a minimum temperature at which no crystals were depositedwas measured once. In the case where it was difficult to judge whethercrystals were deposited, measurement was possibly done two times.

An average value of the measured maximum temperature at which crystalswere deposited inside the glass and the measured minimum temperature atwhich no crystals were deposited was determined as a glass internaldevitrification temperature T_(d).

(Internal Devitrification Viscosity η_(d))

A glass internal devitrification temperature T_(d) was determined by theabove method and glass internal devitrification viscosity η_(d) wasdetermined by measuring glass viscosity at the glass internaldevitrification temperature T_(d).

(Crystal Growth Rate)

Pulverized glass particles are put into a platinum dish and heat-treatedfor 17 hours in an electric furnace that is controlled around a surfacedevitrification temperature, thereby producing plural primary crystalsamples in which minute primary crystals are deposited in the glasssurface. The produced primary crystal samples are held for 1-4 hours attemperatures having intervals 20° C. in such a temperature range thatthe glass viscosity is 10⁴-10⁶ dPa·s, thereby growing crystals at therespective holding temperatures. Lengths of longest portions of crystalgrains obtained before and after the holding at each holding temperaturewere measured, a difference between the crystal sizes obtained beforeand after the holding at each holding temperature was determined, and acrystal growth rate at each holding temperature was determined bydividing the crystal size difference by the holding time. A maximumvalue of the growth rates in such a temperature range that the glassviscosity became 10⁴-10⁶ dPa·s was employed as a crystal growth rate.

(Etching Rate)

Raw materials of respective components were mixed so as to obtain eachof target glass compositions shown in Tables 1 and 2, melted in anelectric furnace, and clarified, thereby obtaining each alkali-freeglass base material. Each alkali-free glass base material wasmirror-polished, cut into an alkali-free glass substrate 1 of 20 mm×30mm×0.5 mm (thickness), cleaned, dried, and subjected to a massmeasurement.

An aqueous solution (liquid chemical) adjusted so as to contain 5 mass %hydrofluoric acid and 2 mass % hydrochloric acid was put into acontainer made of Teflon (registered trademark) and held at 40° C. usinga constant temperature bath. The entire alkali- free glass substrate wasimmersed in the liquid chemical for 20 minutes. The immersed alkali-freeglass substrate was cleaned by pure water and dried, and then subjectedto a mass measurement.

A surface area was calculated from the sample dimensions and an etchingrate per unit time was calculated by dividing, by the surface area, aquotient obtained by dividing a mass reduction by a density and thendividing a resulting quotient by the immersion time.

(Sludge Volume)

The entire alkali-free glass substrate 1 that was used for calculatingan etching rate was again immersed in the liquid chemical of 40° C. andmelted completely. After 1.8 ml of 50 mass % hydrofluoric acid was addedto the above liquid chemical to compensate for hydrofluoric acidconsumed by the etching, a new alkali-free glass substrate 2 of 20 mm×30mm×0.5 mm (thickness) was immersed in the liquid chemical and alsomelted completely.

Furthermore, after 1.8 ml of 50 mass % hydrofluoric acid was added tothe above liquid chemical, a new alkali-free glass substrate 3 of 20mm×30 mm×0.5 mm (thickness) was immersed in the liquid chemical andmelted completely according to the same procedure. The liquid chemicalin which the alkali-free glass substrate 3 had been melted was held forone day and night (24 hours) while being stirred by a magnetic stirrer,thereby producing sludge (insoluble matter) in the liquid chemical. Toprevent evaporation of the liquid chemical, a lid made of Teflon(registered trademark) was put on the container during the test.Subsequently, the liquid chemical and sludge contained in the containermade of Teflon (registered trademark) were transferred to a graduatedcylinder and held for 24 hours to precipitate sludge. A volume of thesludge was measured using the scale of the graduated cylinder andemployed as a sludge volume.

(Specific Modulus)

The specific modulus is determined by dividing the Young's modulusdetermined in the above-described procedure by the density.

TABLE 1 mol % Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 SiO₂ 68.768.4 69.5 70.0 65.0 68.5 65.8 64.2 Al₂O₃ 11.5 13.2 12.5 12.0 12.7 12.19.8 14.0 B₂O₃ 1.8 2.1 2.7 1.2 2.6 3.0 2.8 1.5 MgO 8.4 7.8 7.5 7.7 9.66.5 11.3 9.7 CaO 5.0 4.8 3.8 4.5 5.8 3.3 7.2 4.2 SrO 1.8 3.2 2.3 3.0 3.83.3 3.1 6.4 BaO 2.8 0.5 1.7 1.6 0.5 3.3 0.0 0.0 RO 18.0 16.3 15.3 16.819.7 16.4 21.6 20.3 MgO/CaO 1.68 1.63 1.97 1.71 1.66 1.97 1.57 2.31Value of formula (A) 83.9 85.0 82.7 84.3 86.7 81.1 86.4 88.6 Value offormula (B) 720 725 723 732 704 715 688 714 Value of formula (C) −17.928.2 −16.7 −30.5 74.6 −9.7 −14.7 110.3 Value of formula (D) 7.50 6.812.11 6.09 15.86 8.55 11.72 22.17 Value of formula (E) 3.41 3.43 2.832.75 5.11 3.87 4.00 5.96 Average thermal expansion 38.8 36.0 35.5 37.241.5 (38.9) 40.9 (41.8) coefficient (×10⁻⁷ /° C.) Density (g/cm³) 2.592.54 2.54 2.57 2.57 (2.61) 2.56 (2.63) Strain point (° C.) 706 716 710715 712 (713) 681 (714) Annealing point (° C.) 762 772 767 773 760 (763)(733) (764) Glass transition point (° C.) 755 769 763 769 (760) (767)728 (772) Young's modulus (GPa) 84.2 86.1 83.4 84.3 85.0 (81) 86.4 (89)T₂ (° C.) 1692 1688 1721 1733 1612 (1709) 1601 (1609) T₄ (° C.) 13211323 1339 1349 1268 (1334) 1248 (1274) Surface devitrification temp.T_(c) (° C.) 1245 1295 1305 1265 — — 1275 — Internal devitrificationtemp. T_(d) (° C.) 1195 1255 1225 1235 — — — — Surface devitrificationviscosity η_(c) 10^(4.6) 10^(4.2) 10^(4.3) 10^(4.7) — — 10^(3.8) — (dPa· s) Internal devitrification viscosity η_(d) 10^(5.1) 10^(4.6) 10^(4.9)10^(5.0) — — — — (dPa · s) Crystal growth rate (μm/hr) (≤100) (≤100)(≤100) (≤100) (≤100) (≤100) (≤100) (>100) Sludge volume (ml) (≤30) (≤30)(≤30) (≤30) (≤30) (≤30) (≤30) (>30) Etching rate (μm/min) (2-4.5)(2-4.5) (2-4.5) (2-4.5) (2-4.5) (2-4.5) (2-4.5) (>4.5) Photoelasticconstant (nm/MPa/cm) (27.5) (27.9) (28.5) (27.7) (27.1) (28.1) (27.7)(26.1) Specific modulus (MN · m/kg) 32.5 33.9 32.8 32.8 33.1 (31.1) 33.8(33.7) Equivalent cooling rate (° C./min) 40 40 40 40 40 40 40 40Compaction (ppm) (≤100) (≤100) (≤100) (≤100) (≤100) (≤100) (>100) (≤100)

TABLE 2 mol % Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16SiO₂ 68.5 67.7 69.1 69.5 64.5 68.0 65.4 64.1 Al₂O₃ 11.5 13.1 12.4 11.912.6 12.0 9.8 13.9 B₂O₃ 1.8 2.1 2.7 1.2 2.6 3.0 2.8 1.5 MgO 8.4 7.7 7.57.7 9.5 6.5 11.3 9.7 CaO 5.0 4.8 3.8 4.5 5.8 3.3 7.2 4.2 SrO 1.8 3.2 2.33.0 3.8 3.3 3.1 6.4 BaO 2.8 0.5 1.7 1.6 0.5 3.3 0.0 0.0 Li₂O 0.00 0.000.00 0.02 0.00 0.02 0.00 0.00 Na₂O 0.02 0.03 0.08 0.02 0.05 0.06 0.030.08 K₂O 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.05 F 0.00 0.33 0.17 0.000.17 0.00 0.33 0.00 Cl 0.10 0.53 0.18 0.35 0.35 0.00 0.00 0.00 SnO₂ 0.000.00 0.00 0.10 0.00 0.15 0.00 0.08 SO₃ 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 As₂O₃ 0.00 0.00 0.00 0.00 0.06 0.00 0.00 0.00 Sb₂O₃ 0.00 0.000.00 0.00 0.00 0.02 0.00 0.00 P₂O₅ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 ZrO₂ 0.03 0.03 0.01 0.10 0.03 0.10 0.04 0.00 ZnO 0.00 0.00 0.000.00 0.00 0.23 0.00 0.00 Fe₂O₃ 0.01 0.00 0.02 0.02 0.04 0.02 0.02 0.01β-OH (/mm) 0.25 0.30 0.25 0.40 0.05 0.10 0.45 0.15 RO 18.0 16.3 15.316.8 19.7 16.4 21.6 20.3 MgO/CaO 1.68 1.63 1.97 1.71 1.66 1.97 1.57 2.31Value of formula (A) 83.9 85.0 82.7 84.3 86.7 81.1 86.4 88.6 Value offormula (B) 720 725 723 732 704 715 688 714 Value of formula (C) −17.928.2 −16.7 −30.5 74.6 −9.7 −14.7 110.3 Value of formula (D) 7.50 6.812.11 6.09 15.86 8.55 11.72 22.17 Value of formula (E) 3.41 3.43 2.832.75 5.11 3.87 4.00 5.96 Average thermal expansion 38.8 (36.0) (35.5)(37.2) (41.5) (38.9) (40.9) (41.8) coefficient (×10⁻⁷ / ° C.) Density(g/cm³) 2.59 (2.54) (2.54) (2.57) (2.57) (2.61) (2.56) (2.63) Strainpoint (° C.) 706 (713) (705) (713) (709) (708) (678) (705) Annealingpoint (° C.) 762 (769) (762) (771) (757) (758) (730) (755) Glasstransition point (° C.) 755 (766) (758) (767) (757) (762) (725) (767)Young's modulus (GPa) 84.2 (86) (83) (84) (85) (81) (86) (89) T₂ (° C.)1692 (1688) (1721) (1733) (1612) (1709) (1601) (1608) T₄ (° C.) 1321(1323) (1339) (1349) (1268) (1334) (1248) (1273) Surface devitrificationtemp. T_(c) (° C.) 1245 (1295) (1305) (1265) — — (1275) — Internaldevitrification temp. T_(d) (° C.) 1195 (1255) (1225) (1235) — — — —Surface devitrification viscosity η_(c) (10^(4.6)) (10^(4.2)) (10^(4.3))(10^(4.7)) — — (10^(3.8)) — (dPa · s) Internal devitrification viscosityη_(d) (10^(5.1)) (10^(4.6)) (10^(4.9)) (10^(5.0)) — — — — (dPa · s)Crystal growth rate (μm/hr) (≤100) (≤100) (≤100) (≤100) (≤100) (≤100)(≤100) (>100) Sludge volume (ml) (≤30) (≤30) (≤30) (≤30) (≤30) (≤30)(≤30) (>30) Etching rate (μm/min) (2-4.5) (2-4.5) (2-4.5) (2-4.5)(2-4.5) (2-4.5) (2-4.5) (>4.5) Photoelastic constant (nm/MPa/cm) (27.5)(27.9) (28.5) (27.7) (27.1) (28.1) (27.7) (26.1) Specific modulus (MN ·m/kg) 32.5 (33.9) (32.8) (32.8) (33.1) (31.1) (33.8) (33.7) Equivalentcooling rate (° C./min) 40 40 40 40 40 40 40 40 Compaction (ppm) (≤100)(≤100) (≤100) (≤100) (≤100) (≤100) (>100) (≤100)

In Examples 1-5 and Examples 9-13 in which the value of Formula (A) was82.5 or larger, the Young's modulus was 83 GPa or larger. On the otherhand, in Examples 6 and 14 in which the value of Formula (A) was smallerthan 82.5, the Young's modulus was smaller than 83 GPa.

In Examples 1-5 and Examples 9-13 in which the value of Formula (B) was690 or larger and 800 or smaller, the strain point was 690° C. orhigher. In Examples 7 and 15 in which the value of Formula (B) wassmaller than 690, the strain point was lower than 690° C.

In Examples 1-5 and Examples 9-13 in which the value of Formula (C) was100 or smaller, the crystal growth rate was 100 μm/hr or lower. On theother hand, in Examples 8 and 16 in which the value of Formula (C) waslarger than 100, the crystal growth rate was higher than 100 μm/hr.

In Examples 1-5 and Examples 9-13 in which the value of Formula (D) was20 or smaller, the sludge volume was 30 ml or smaller. On the otherhand, in Examples 8 and 16 in which the value of Formula (D) was largerthan 20, the sludge volume was larger than 30 ml.

In Examples 1-5 and Examples 9-13, the surface devitrification viscosityη_(c) was 10^(4.2) dPa·s or higher. In Examples 7 and 15, the surfacedevitrification viscosity η_(c) was lower than 10^(4.2) dPa·s.

Although the invention has been described in detail with reference tothe particular embodiments, it is apparent to those skilled in the artthat various changes and modifications are possible without departingfrom the spirit and scope of the invention.

The present application is based on Japanese Patent Application No.2019-20257 filed on Feb. 7, 2019, Japanese Patent Application No.2019-51570 filed on Mar. 19, 2019, Japanese Patent Application No.2019-141422 filed on Jul. 31, 2019, Japanese Patent Application No.2019-186805 filed on Oct. 10, 2019, and Japanese Patent Application No.2020-17692 filed on Feb. 5, 2020, the disclosures of which areincorporated herein by reference.

INDUSTRIAL APPLICABILITY

The alkali-free glass according to the invention having theabove-described features are suitable for uses such as substrates fordisplays, substrates for photomasks, substrates for supportingelectronic devices, substrates for information recording media,substrates for planar antennas, substrates for dimming laminates,vehicular window glasses, acoustic vibration plates.

1. An alkali-free glass, comprising, in mol % in terms of oxides: SiO₂:63-75%; Al₂O₃: 10-16%; B₂O₃: larger than 0.5% and 5% or smaller; MgO:0.1-15%; CaO: 0.1-12%; SrO: 0-8%; and BaO: 0-6%, wherein: [MgO]/[CaO] islarger than 1.5; a value of Formula (A) is 82.5 or larger, Formula (A)being1.131[SiO₂]+1.933[Al₂O₃]+0.362[B₂O₃]+2.049[MgO]+1.751[CaO]+1.471[SrO]+1.039[BaO]−48.25;a value of Formula (B) is 690 or larger and 800 or smaller, Formula (B)being35.59[SiO₂]+37.34[Al₂O₃]+24.59[B₂O₃]+31.13[MgO]+31.26[CaO]+30.78[SrO]+31.98[BaO]−2761;a value of Formula (C) is 100 or smaller, Formula (C) being−9.01[SiO₂]+36.36[Al₂O₃]+5.7[B₂O₃]+5.13[MgO]+17.25[CaO]+7.65[SrO]+10.58[BaO];a value of Formula (D) is 20 or smaller, Formula (D) being{−0.731[SiO₂]+1.461[Al₂O₃]−0.157[B₂O₃]+1.904[MgO]+3.36[CaO]+3.411[SrO]+1.723[BaO]+(−3.318[MgO][CaO]−1.675[MgO][SrO]+1.757[MgO][BaO]+4.72[CaO][SrO]+2.094[CaO][BaO]+1.086[SrO][BaO])}/([MgO]+[CaO]+[SrO]+[BaO]);and the alkali-free glass has a Young's modulus of 83 GPa or larger anda surface devitrification viscosity η_(c) of 10^(4.2) dPa·s or higher.2. The alkali-free glass according to claim 1, wherein a value ofFormula (E) is in a range of 1.50 to 5.50, Formula (E) being4.379[SiO₂]+5.043[Al₂O₃]+4.805[B₂O₃]+4.828[MgO]+4.968[CaO]+5.051[SrO]+5.159[BaO]−453.3. The alkali-free glass according to claim 1, having a strain point of690° C. or higher.
 4. The alkali-free glass according to claim 1, havinga density of 2.8 g/cm³ or lower and an average thermal expansioncoefficient in 50-350° C. of 30×10⁻⁷/° C. to 45×10⁻⁷/° C.
 5. Thealkali-free glass according to claim 1, having a temperature T₂ at whicha glass viscosity becomes 10² dPa·s of 1800° C. or lower and atemperature T₄ at which the glass viscosity becomes 10⁴ dPa·s of 1400°C. or lower.
 6. The alkali-free glass according to claim 1, having aninternal devitrification temperature of 1320° C. or lower.
 7. Thealkali-free glass according to claim 1, having an internaldevitrification viscosity η_(d) of 10^(4.4) dPa·s or higher.
 8. Thealkali-free glass according to claim 1, having a crystal growth rate of100 μm/hr or lower.
 9. The alkali-free glass according to claim 1,comprising at least one selected from the group consisting of Li₂O,Na₂O, and K₂O in an amount of 0.2% or smaller in total in mole % interms of oxides.
 10. An alkali-free glass, comprising, in mol % in termsof oxides: SiO₂: 50-80%; Al₂O₃: 8-20%; Li₂O+Na₂O+K₂O: 0-0.2%, and P₂O₅:0-1%, wherein [MgO]/[CaO] is larger than 1.5, and the alkali-free glasshas: a Young's modulus of 83 GPa or larger; a strain point of 690° C. orhigher; a temperature T₄ at which a glass viscosity becomes 10⁴ dPa·s of1400° C. or lower; a temperature T₂ at which the glass viscosity becomes10² dPa·s of 1800° C. or lower; an internal devitrification temperatureof 1320° C. or lower; an internal devitrification viscosity η_(d) of10^(4.4) dPa·s or higher; a surface devitrification viscosity η_(c) of10^(4.2) dPa·s or higher; a crystal growth rate of 100 μm/hr or lower; adensity of 2.8 g/cm³ or lower; a specific modulus of 31 or higher; andan average thermal expansion coefficient in 50-350° C. of 30×10⁻⁷ to45×10⁻⁷/° C.
 11. The alkali-free glass according to claim 10, comprisingB₂O₃ in an amount of 0-5% in mol % in terms of oxides.
 12. Thealkali-free glass according to claim 10, comprising, in mol % in termsof oxides: MgO: 0.1-15%; CaO: 0.1-12%; SrO: 0-8%; and BaO: 0-6%.
 13. Thealkali-free glass according to claim 10, comprising, in mol % in termsof oxides: B₂O₃: 0-5%; MgO: 0.1-15%; CaO: 0.1-12%; SrO: 0-8%; and BaO:0-6%.
 14. The alkali-free glass according to claim 10, wherein a valueof Formula (A) is 82.5 or larger, Formula (A) being1.131[SiO₂]+1.933[Al₂O₃]+0.362[B₂O₃]+2.049[MgO]+1.751[CaO]+1.471[SrO]+1.039[BaO]−48.25.15. The alkali-free glass according to claim 10, wherein a value ofFormula (B) is 690 or larger and 800 or smaller, Formula (B) being35.59[SiO₂]+37.34[Al₂O₃]+24.59[B₂O₃]+31.13[MgO]+31.26[CaO]+30.78[SrO]+31.98[BaO]−2761.16. The alkali-free glass according to claim 10, wherein a value ofFormula (C) is 100 or smaller, Formula (C) being−9.01[SiO₂]+36.36[Al₂O₃]+5.7[B₂O₃]+5.13[MgO]+17.25[CaO]+7.65[SrO]+10.58[BaO].17. The alkali-free glass according to claim 10, wherein a value ofFormula (D) is 20 or smaller, Formula (D) being{−0.731[SiO₂]+1.461[Al₂O₃]−0.157[B₂O₃]+1.904[MgO]+3.36[CaO]+3.411[SrO]+1.723[BaO]+(−3.318[MgO][CaO]−1.675[MgO][SrO]+1.757[MgO][BaO]+4.72[CaO][SrO]+2.094[CaO][BaO]+1.086[SrO][BaO])}/([MgO]+[CaO]+[SrO]+[BaO]).18. The alkali-free glass according to claim 10, wherein a value ofFormula (E) is 1.50-5.50, Formula (E) being4.379[SiO₂]+5.043[Al₂O₃]+4.805[B₂O₃]+4.828[MgO]+4.968[CaO]+5.051[SrO]+5.159[BaO]−453.
 19. The alkali-free glass according to claim 1,comprising F in an amount of 1.5 mol % or smaller.
 20. The alkali-freeglass according to claim 1, comprising SnO₂ in an amount of 0.5% orsmaller in mol % in terms of oxides.
 21. The alkali-free glass accordingto claim 1, comprising ZrO₂ in an amount of 0.09% or smaller in mol % interms of oxides.
 22. The alkali-free glass according to claim 1, whereina glass β-OH value is 0.01 mm⁻¹ or larger and 0.5 mm⁻¹ or smaller. 23.The alkali-free glass according to claim 1, having an annealing point of850° C. or lower.
 24. The alkali-free glass according to claim 1,wherein a compaction is 150 ppm or smaller when being held at 600° C.for 80 min.
 25. The alkali-free glass according to claim 1, having anequivalent cooling rate of 5° C./min or higher and 800° C./min or lower.26. The alkali-free glass according to claim 1, wherein a sludge volumewhen the glass is subjected to an etching process is 30 ml or smaller.27. The alkali-free glass according to claim 1, having a photoelasticconstant of 31 nm/MPa/cm or smaller.
 28. A glass plate comprising thealkali-free glass according to claim 1, having a length of at least oneside of 2400 mm or longer and a thickness of 1.0 mm or smaller.
 29. Theglass plate according to claim 28, manufactured by a float process or afusion process.
 30. A display panel, comprising the alkali-free glassaccording to claim
 1. 31. A semiconductor device, comprising thealkali-free glass according to claim
 1. 32. An information recordingmedium, comprising the alkali-free glass according to claim
 1. 33. Aplanar antenna, comprising the alkali-free glass according to claim 1.34. A dimming laminate, comprising the alkali-free glass according toclaim
 1. 35. A vehicular window glass, comprising the alkali-free glassaccording to claim
 1. 36. An acoustic vibration plate, comprising thealkali-free glass according to claim
 1. 37. The alkali-free glassaccording to claim 10, comprising F in an amount of 1.5 mol % orsmaller.
 38. The alkali-free glass according to claim 10, comprisingSnO₂ in an amount of 0.5% or smaller in mol % in terms of oxides. 39.The alkali-free glass according to claim 10, comprising ZrO₂ in anamount of 0.09% or smaller in mol % in terms of oxides.
 40. Thealkali-free glass according to claim 10, wherein a glass β-OH value is0.01 mm⁻¹ or larger and 0.5 mm⁻¹ or smaller.
 41. The alkali-free glassaccording to claim 10, having an annealing point of 850° C. or lower.42. The alkali-free glass according to claim 10, wherein a compaction is150 ppm or smaller when being held at 600° C. for 80 min.
 43. Thealkali-free glass according to claim 10, having an equivalent coolingrate of 5° C./min or higher and 800° C./min or lower.
 44. Thealkali-free glass according to claim 10, wherein a sludge volume whenthe glass is subjected to an etching process is 30 ml or smaller. 45.The alkali-free glass according to claim 10, having a photoelasticconstant of 31 nm/MPa/cm or smaller.
 46. A glass plate comprising thealkali-free glass according to claim 10, having a length of at least oneside of 2400 mm or longer and a thickness of 1.0 mm or smaller.
 47. Theglass plate according to claim 46, manufactured by a float process or afusion process.
 48. A display panel, comprising the alkali-free glassaccording to claim
 10. 49. A semiconductor device, comprising thealkali-free glass according to claim
 10. 50. An information recordingmedium, comprising the alkali-free glass according to claim
 10. 51. Aplanar antenna, comprising the alkali-free glass according to claim 10.52. A dimming laminate, comprising the alkali-free glass according toclaim
 10. 53. A vehicular window glass, comprising the alkali-free glassaccording to claim
 10. 54. An acoustic vibration plate, comprising thealkali-free glass according to claim 10.